A communication system as a successor of W-CDMA and HSDPA, namely, Long Term Evolution (LTE) has been considered by a W-CDMA standardization organization 3GPP. As a radio access scheme, Orthogonal Frequency Division Multiplexing (OFDM) is under consideration for downlink, and Single-Carrier Frequency Division Multiple Access (SC-FDMA) is under consideration for uplink (see 3GPP TR 25.814 (V7.0.0), “Physical Layer Aspects for Evolved UTRA”, June 2006, for example).
In OFDM, a frequency band is divided into plural narrow frequency bands (sub-carriers), and data are placed on the respective divided frequency bands to carry out transmission. The sub-carriers are densely arranged in a frequency direction, allowing the sub-carriers to be partly overlapped without causing interference, thereby realizing high speed transmission and improving frequency usage efficiency.
In SC-FDMA, a frequency band is divided into plural narrow bands, and different narrow bands are used by different user terminals, so that interference between the user terminals can be reduced. According to SC-FDMA, which is characterized in that variations in the transmission power are reduced, a large coverage area and low energy consumption can be realized.
In the conventional W-CDMA uplink, which is characterized by a non-orthogonal system, all channels use the same frequency band, namely, the whole system band for communications. For example, a random access channel (RACH), which is used for establishing an initial connection in uplink, employs the combination of code-multiplexing and time-multiplexing schemes to carry out transmission in the system. The random access channel is also called a contention-based channel. A mobile station can use the random access channel at any timing in order to indicate its request for resource allocation.
In the W-CDMA system, as described above, both typical data channels and the random access channel use the same frequency band, namely, the whole system band. In addition, these channels are transmitted without orthogonalization. Thus, resources in the frequency direction are not managed for the typical data channels and the random access channel. When the amount of uplink interference is measured, the amount of interference for the whole system band including all channels is measured. Thus, the amount of interference for the random access channel need not be distinguished from the amount of interference for the typical data channels.
In the LTE system, as described above, SC-FDMA which is under consideration for the uplink radio access scheme is characterized by an orthogonal system. In SC-FDMA, a random access channel and typical data channels use mutually different frequency bands for transmission.